Refined Iron

Overview
Refined Iron is a material produced when combining Iron Ore, and Heat.

Refined Iron is used in many early-game recipes, such as the Forge, the Iron Gear (Which allows for building of the Mill and the Lumbermill), the Iron Compost Bin, etc.

Iron Ore is most commonly found on Mainland, Rockma, Magma, Spire, Cenote, Rockshard and Plateau. It is also found at Volcano and Crescent, but at much smaller quantities. The easiest place for Iron would most likely be Rockma, as a torch is not required.

Trivia

 * A strange and unconventional way to obtain Refined Iron is by placing burning large or small leaves on top of an Iron Ore vein. This smelts the Iron Ore into Refined Iron, but mining it is still required.
 * This is the most common ore in the game, being found on more islands than any other ore (although Coal may actually have around the same)